anticorpos: estrutura e função antígenos reações entre ... · suas interações com antigenos?...
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Anticorpos: Estrutura e FunçãoAntígenos
Reações entre Antígenos e AnticorposAplicações
Profa. Isabel [email protected]. 153267
A Natureza dos Anticorpos
Pesquisadores injetavam coelhos com diferentes antígenos
proteínas solúveis, bactérias, hemácias heterólogas....
Obtinham:• Precipitinas• Lisinas• Aglutininas• Opsoninas
PerguntasEstruturas diferentes para cada função?
XTeoria Unitária?
Desenvolvimento do Modelo da Imunoglobulina de Quatro Cadeias
Rodney Porter tratou anticorpos com a enzima papaína e obteve três fragmentos, dois dos quais se ligavam a antígenos, cada um contendo um único sítio de ligação, e o outro fragmento se cristalizou
George Edelman tratou anticorpos com agente redutor que quebra pontes de dissulfeto e obteve indícios de que os anticorpos continham ao menos dois tipos de cadeia
Nisonoff tratou tratou anticorpos com a enzima pepsina e obteve um fragmento com dois sítios de ligação com antígenos e vários peptídeos pequenos
Proteolytic fragments of an IgG moleculeUnraveling structure and function
Structure of an antibody molecule.
The hinge region of the immunoglobulin molecule allows flexibility in binding to multiple antigens.
Adiante: Classes e subclasses de Igs
immunoglobulin-like domains: present in many proteins of the immune system (KIRs of NK cells; involved in cell–cell recognition and adhesion. Together with the immunoglobulins and the T-cell receptors, these proteins make up the extensive immunoglobulin superfamily
O sítio de ligação com antígenos
Hypervariable regions in Ig moleculesWu-Kabat Plots
The interaction of the antibody molecule with specific antigen.
The hypervariable regions lie in discrete loops of the folded structure.
Structure of an Ig domain
Binding of an antigen by an antibody
The constant region confers functional specialization on the antibody.
Human Antibody Isotypes
Human Antibody Isotypes
aDepends onallotype. bForA/Aisomer. cMultivalent binding to transfected cells. Adapted from Bruhnsetal.(2). dAssociation constant (X 106 M-1) for monovalent binding (2). eAfter repeated encounters with protein antigens, often allergens.
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IgG facts and figures
Heavy chains: g 1 g 2 g3 g4 - Gamma 1 - 4
Half-life: IgG1 21 - 24 days IgG2 21 - 24 days
IgG3 7 - 8 days IgG4 21 - 24 days
Serum level (mgml-1): IgG1 5 - 12 IgG2 2 - 6
IgG3 0.5 - 1 IgG4 0.2 - 1
% of Ig in serum: IgG1 45 - 53 IgG2 11 - 15
IgG3 3 - 6 IgG4 1 - 4
Complement activation: IgG1 +++ IgG2 +
IgG3 ++++ IgG4 No
Interactions with cells: All subclasses via IgG receptors on macrophages
and phagocytes
Transplacental transfer: IgG1 ++ IgG2 +
IgG3 ++ IgG4 ++
FcRn contributes to the long half-life of IgG molecules
Flexibility of antibody molecules
Membrane and secreted forms of Ig heavy chains
Idiotype network: a form of immunoregulation?
Antibodies bind to conformational shapes on the surfaces of antigens using a variety of noncovalent forces.
Antigens can bind in pockets, or grooves, or on extended surfaces in the binding sites of antibodies.
The nature of antigenic determinants
The dose of antigen used in an initial immunization affects the primary and the secondary antibody response.
Antibodies can be elicited by small chemical groups called
haptens only when the hapten is linked to an
immunogenic protein carrier.
Valency and avidity of antibody-antigen interactions
Antigen-antibody complexesThe basis of immunopathology of immune-mediated diseases
Changes in antibody structure during humoral immune responses
Ig expression during B lymphocyte maturation
Propriedades das Igs dependem do tipo e nível de glicosilação
Crystal structure of na human IgG1 molecule viewed from two different angles, demonstrating theflexibility of
the two Fab fragments with respect to each other and the Fc tail.
The N-linked glycan found at position 297 can be found as a core structure, common to all IgG found in human
beings and rodents (core structure indicated with a red dashed line)
Propriedades das Igs dependem do tipo e nível de glicosilação
• Type 2 diabetes mellitus is a common complication of obesity• Activation of the IgG receptor FcgRIIB in endothelium by hyposialylated IgG has a role
in obesity-induced insulin resistance• Despite becoming obese on a high-fat diet, mice lacking FcgRIIB globally or selectively
in endothelium were protected from insulin resistance (insulin delivery to skeletal muscle and resulting maintenance of muscle glucose disposal)
• IgG transferred from patients with T2DM but not from metabolically healthy subjects caused insulin resistance in IgG-deficient mice via FcgRIIB
• IgG from T2DM patients was hyposialylated. • In HFD-fed mice, supplementation with a sialic acid precursor restored IgG sialylation
and preserved insulin sensitivity without affecting weight gain.
University of Texas Southwestern Medical Center, Dallas, Texas, USA
N-acetil-D-manosamina (ManNAc) é precursor de ácido siálico
Some species generate antibodies with alternative structures.
Editorial Summary - Milking cows for their antibodiesHIV infection gives rise to the generation of broadly neutralizing antibodies in a subset of infected subjects. However, it has been difficult to induce such antibodies through vaccination in humans and a variety of animal models. Four cows were immunized with a recombinant HIV envelope protein and broadly neutralizing antibodies developed rapidly after repeated immunization. For example, one cow developed cross-neutralizing activity just 42 days after a vaccine boost.
Effector functions of antibodies
Como detectar e medir Anticorpos e suas interações com Antigenos?
Antígenos particulados - Aglutinação
The Ouchterlony reaction: • Detect, identify, and quantify
antibody and antigen• Test the similarity between antigens
• For disease diagnosis
Antígenos solúveis - Precipitação
The Coombs direct and indirect anti-globulin tests for antibody against red blood cell antigens.